Helical fine structure, method for producing the same, and electric-wave shield or absorber using the helical fine structure

ABSTRACT

A helical fine structure of the present invention is characterized by including: a phytoplankton having a helical shape and selected from a group of cyanobacteria called  Spirulina ; and a surface modification layer formed on the phytoplankton. The surface modification layer includes at least one metal plating layer. Thereby, the helical fine structure can be utilized as an electric-wave shield or an absorber. Moreover, a method for producing the helical fine structure is characterized in that a prestep of a step of forming the surface modification layer on the phytoplankton having a helical shape includes a washing step with an organic solvent to remove an outer membrane from a surface of the phytoplankton.

TECHNICAL FIELD

The present invention relates to a fine structure having a helicalshape, and particularly relates to a helical fine structure applicableto an electric-wave (a radio-wave) shield or absorbing material.

BACKGROUND ART

In order to make observation with an electron microscope easy bypreventing electrification due to irradiation of an electron beam,generally, a conductive film has been heretofore formed on the surfaceof a microorganism sample or the like having no conductivity. Thispractice serves as a motivation for forming a conductive film on atissue surface of a microorganism for industrial application. However,the practice does not necessarily suggest specifically on what parts ofwhat microorganism species, and for what applications, its benefits canbe obtained by forming the conductive film.

Meanwhile, regarding an application of a conductive structure having ahelical shape as an electric-wave (a radio-wave) shield or an absorber,JP-A 2000-027072 (Patent Document 1) discloses an example in which ahelical carbon deposit formed by a vapor deposition method is utilizedas an electric-wave shield or an absorber. However, the shape of thecarbon deposit formed by the vapor deposition method varies due toinfluences of the concentration of a raw-material gas in a reactor or ona substrate, the composition of the raw-material gas, the temperaturedistribution, and the like. It is extremely difficult to efficientlygrow a deposit having an orderly helical shape.

To avoid such instability of the vapor deposition method, JP-A2009-221149 (Patent Document 2) discloses a method in which a piece of avessel secondary wall having a helical shape is taken out from avascular plant, and a conductive film is formed on the surface thereoffor use as an electric-wave shield or an absorber. However, in theprocess of taking out the piece of the vessel secondary wall having ahelical shape from the vascular plant, since an unnecessary portionaround the piece has to be removed by a large amount, the raw materialefficiency is low. In addition, to remove the unnecessary portion, alarge amount of chemicals has to be introduced, and long processing timeis required. For this reason, a more efficient production method hasbeen demanded.

DISCLOSURE OF THE INVENTION

The present invention has been made by focusing on such problems. Anobject of the present invention is to provide a helical fine structurecapable of efficient mass production.

In this connection, the present inventors have made studies on thematerial suitable for a helical fine structure capable of massproduction. As a result, the inventors have found an approach employinga phytoplankton which does not particularly require removal of anunnecessary portion therefrom.

Specifically, the helical fine structure according to the presentinvention is characterized by including: a phytoplankton having ahelical shape; and a surface modification layer formed on thephytoplankton. Moreover, the helical fine structure is characterized inthat the surface modification layer includes at least one metal platinglayer. Note that the phytoplankton on which the surface modificationlayer is formed may be in any state with an outer membrane remained on asurface thereof and thus unremoved therefrom, or with the outer membranebeing removed. Further, the helical fine structure is characterized inthat the phytoplankton having a helical shape is a phytoplanktonselected from the group of cyanobacteria called Spirulina and includingArthrospira Platensis, Arthrospira Maxima, and Arthrospira Subsalsabelonging to Arthrospira genus.

Next, a method for producing the helical fine structure is characterizedin that a prestep of a step of forming the surface modification layer onthe phytoplankton having a helical shape includes a step of removing theouter membrane from the surface of the phytoplankton. Moreover, themethod for producing the helical fine structure is characterized in thatthe step of removing the outer membrane from the surface of thephytoplankton is a washing step with an organic solvent. Further, themethod for producing the helical fine structure is characterized byincluding: a drying step of drying the phytoplankton having a helicalshape to obtain a deformed dried phytoplankton; and a shape recoveringstep of permeating the dried phytoplankton with a polar solvent to causethe phytoplankton to recover the same helical shape as before the dryingstep.

Furthermore, an electric-wave shield or an absorber according to thepresent invention is characterized by including multiple helical finestructures in each of which a surface modification layer including atleast one metal plating layer is formed on a phytoplankton having ahelical shape, the helical fine structures electrically or magneticallyconnected together to form an assembly.

As described above, the helical fine structure of the present inventionincludes the phytoplankton having a helical shape on which the surfacemodification layer is formed. Moreover, unlike a vascular plantdescribed in the previous section, the phytoplankton employed in thehelical fine structure of the present invention is a material which doesnot particularly require removal of an unnecessary portion therefrom.Accordingly, efficient production is possible. Further, the surfacemodification layer including at least one metal plating layer producesan effect that the helical fine structure can be utilized as anelectric-wave shield or an absorber.

BEST MODES FOR PRACTICING THE INVENTION

Embodiments of the present invention are described below in detail.

In the present invention, a helical fine structure usable for variousapplications is obtained by forming a surface modification layer on aphytoplankton having a helical shape. Examples of the species of thephytoplankton used as the raw material include the group ofcyanobacteria generally called Spirulina and consisting of ArthrospiraPlatensis, Arthrospira Maxima, and Arthrospira Subsalsa belonging to thegenus Arthrospira. The number of turns in the helix during the growth ofa Spirulina individual is 5 to 10. The typical dimensions of Spirulinaare: 300 to 500 μm in length measured in the axial direction andapproximately 50 μm in diameter.

As the surface modification layer, a conductive layer is formed by metalplating, for example. Thus, a microcoil that is a small electricalelement is formed. In a case where a conductive microcoil having thesame typical dimension values as described above is formed, theself-resonant frequency of the single microcoil formed with a straycapacitance is in the region of 100 GHz to 1 THz. Thus, the microcoilcan be used as an electric-wave shield or an absorber having a resonanceabsorption function with respect to an electromagnetic wave in thisregion.

Moreover, if the microcoil is brought into contact with and electricallyconnected to a microcoil of the same type, both equivalent coil lengthand parasitic capacitance are increased. Thus, the resonant frequencyrange can be extended to a lower frequency region. To surely connect themicrocoils electrically, the plating film should be formed in acondition where multiples of Spirulina are connected to each other.

For example, by immersing a group of Spirulina in ethyl alcohol, thecondition where the multiples of Spirulina are connected to each othercan be obtained. When an outer membrane of Spirulina is disintegratedand removed with ethyl alcohol, a matter thus disintegrated and removedand an effluent from the cell form a mucus-like substance that helps alarge number of Spirulina to aggregate therearound. By subjecting thisaggregate to a plating treatment, the microcoils connected to each othercan be produced.

As another means for electrically connecting the microcoils, there is amethod in which an external magnetic field is applied to magnetizedmicrocoils so that the microcoils can be connected to each other. Agroup of Spirulina is prepared in which a magnetized layer such as a Niplating layer is formed on the surface of each of the Spirulinaindividuals. Then, the group is assembled with fibers such as, forexample, pulp, while an external magnetic field is being appliedthereto. Thereby, a network of microcoils connected to each other can bemixed within the pulp fibers. By molding this assembly into a sheet formfollowed by drying, a papery electric-wave shield or absorber can beproduced.

Note that the microcoils do not necessarily have to be connected to eachother in a state of conductive contact in a strict sense. If themultiple microcoils are close to each other at a small distance, themicrocoils are magnetically connected to each other by mutualinductance, and an extended line is formed. This can produce an effectthat the resonant frequency range is extended to a lower region. Forexample, if a powder of the microcoil is dispersed in a thermosettingepoxy resin, this product can be used as an ink paste. A film coatedwith this paste and cured by heating works as an electric-wave shield oran absorber having favorable loss characteristics in the frequencyregion of, for example, 1 to 10 GHz.

Further, in order to extend the frequency range to a lower frequencyregion, it is effective to dispose a high dielectric material around thecoil. For example, a film made of a ferroelectric material may be formedon the surface of each coil. In a case of the aforementioned paperyelectric-wave shield or absorber, the film made of a ferroelectricmaterial may be formed on the mixed fiber.

Meanwhile, in the conventional usage of Spirulina, such as food, feed,and raw material of a pigment, harvested Spirulina is pulverized bydry-crushing, or molded into an aggregate in a pellet form, for example.In this processing, the helical shape of the Spirulina individuals isdestroyed. This is because the target in the conventional usage ofSpirulina is mostly the components of its content. Accordingly, theimportance of retaining the helical shape of the Spirulina individualsis not recognized in the processing into the dried form suitable formeasurement, transportation, and storage.

Spirulina loses its helical shape as deformed by drying withoutpulverizing or pelletizing. Normally, Spirulina floats in a cultureliquid or the like and keeps its helical shape. However, whensurrounding water is removed, Spirulina is squashed due to deformationby its own weight and then dried into a planar zigzag shape. Thus, inthe usage of Spirulina according to the present invention, it is quiteuseful to obtain Spirulina in a dry form which is suitable formeasurement, transportation, and storage, and which still enables thehelical shape to be retained.

In this connection, the present inventors have made earnest experimentsto reveal the characteristics of Spirulina and its dried product. As aresult, the inventors have found out that even if Spirulina is squasheddue to deformation by its own weight and dried in a planar zigzag shape,imbibition with a polar solvent such as water and alcohols permeableinto a hydrophilic tissue of dried Spirulina allows recovering of thedimensional helical shape. This eliminates the need to dry and keep thehelical shape by a method such as freeze-drying that requires adedicated device. Thus, the processing can be performed inexpensively inlarge amounts using a simple device.

In addition, the present inventors have found out that when Spirulina isdried, a crack is formed into a cell wall of Spirulina. Through thiscrack, liquids such as water and alcohols used in the subsequent shaperecovering step can readily permeate a tissue of dried Spirulina.Effective components including nutrients such as various amino acids,pigments such as chlorophyll, phycocyanin and carotenoid, and the likeare efficiently extracted into these liquids. This makes effectiveutilization of the resources possible.

Note that in the aforementioned step of disintegrating and removing theouter membrane of Spirulina with ethyl alcohol also, the effectivecomponents including nutrients, pigments, and the like are extractedinto ethyl alcohol. Moreover, exactly the same shape recovery asdescribed above is exhibited also in a case of drying Spirulina fromwhich the outer membrane has been removed. Thus, remaining effectivecomponents can be further extracted in the shape recovering step.

The present invention will be described below in detail based onExamples. Note that in Examples illustrated below, Arthrospira Platensiswas selected as the Spirulina species.

EXAMPLE 1

In order to eliminate a problem arising from various kinds of ionsremaining in a culture liquid in the subsequent step, filter-washing wasperformed using running water while Spirulina was being held by a meshfilter having an opening size of 25 μm or smaller. Then, Spirulina wasintroduced into ethyl alcohol to remove an outer membrane thereof. Themucosa-like outer membrane lysates were assembled to form a large numberof floating pieces, and portions of the cytoplasm and pigments wereeluted into ethyl alcohol. The solution containing the mixture of thesewas passed through a coarse mesh filter having an opening size of 250 μmor larger. Spirulina was passed therethrough, while the cytoplasm andthe outer membrane lysates were trapped. Ethyl alcohol containingSpirulina thus passed was separated from ethanol containing the pigmentcomponent with a fine mesh filter having an opening size of 25 μm orsmaller. Thereby, Spirulina was trapped.

Ni plating was performed on trapped Spirulina according to the followingprocedure.

First, Spirulina was introduced into an aqueous solution containing acatalyst (manufactured by Meltex Inc, product name: Melplate activator7331). The catalyst was attached to Spirulina floating in the solution.Then, the mixture was introduced into a Ni plating solution(manufactured by Meltex Inc, product name: Melplate NI-871), andelectroless Ni plating (i.e., modification treatment including coatingtreatment) was performed while the Spirulina was again floating in thesolution. The thickness of the Ni plating layer was approximately 1 μm.According to the procedure described above, a conductive helical finestructure having an average diameter of approximately 0.05 mm and anaverage length of approximately 0.5 mm was obtained.

EXAMPLE 2

In order to eliminate a problem arising from various kinds of ionsremaining in a culture liquid in the subsequent steps, filter-washingwas performed using running water while Spirulina was being held by amesh filter having an opening size of 25 μm or smaller. Then, Spirulinawas introduced into ethyl alcohol to remove an outer membrane thereof.The multiple Spirulina individuals were connected to each other with themucosa-like outer membrane lysates to form a Spirulina assembly. Inaddition, portions of the cytoplasm and pigments were eluted into ethylalcohol. The solution containing the mixture of these was passed througha fine mesh filter having an opening size of 25 μm or smaller, andseparated from ethanol containing the pigment component. Thereby, theSpirulina assembly was trapped.

Ni plating was performed on the trapped Spirulina assembly according tothe following procedure.

First, the Spirulina assembly was introduced into an aqueous solutioncontaining a catalyst (manufactured by Meltex Inc, product name:Melplate activator 7331). The catalyst was attached to the Spirulinaassembly floating in the solution. Then, the mixture was introduced intoa Ni plating solution (manufactured by Meltex Inc, product name:Melplate NI-871), and electroless Ni plating (i.e., modificationtreatment including coating treatment) was performed while the Spirulinaassembly was again floating in the solution. The thickness of the Niplating layer was approximately 1 μm. According to the proceduredescribed above, a microcoil assembly was obtained which was anaggregate of multiple microcoils each having dimensions: an averagediameter of approximately 0.05 mm and an average length of approximately0.5 mm.

EXAMPLE 3

In order to eliminate a problem arising from various kinds of ionsremaining in a culture liquid in the subsequent steps, filter-washingwas performed using running water while Spirulina was being held by amesh filter having an opening size of 25 μm or smaller. Then, Spirulinawas introduced into ethyl alcohol to remove an outer membrane thereof.The mucosa-like outer membrane lysates were assembled to form a largenumber of floating pieces, and portions of the cytoplasm and pigmentswere eluted into ethyl alcohol. The solution containing the mixture ofthese was passed through a coarse mesh filter having an opening size of250 μm or larger. Spirulina was passed therethrough, while the cytoplasmand the outer membrane lysates were trapped. Ethyl alcohol containingSpirulina thus passed was separated from ethanol containing the pigmentcomponent with a fine mesh filter having an opening size of 25 μm orsmaller. Thereby, Spirulina was trapped.

The trapped Spirulina individuals were dried with hot air to obtaindried Spirulina suitable for measurement, transportation, and storage.The dried Spirulina thus obtained was introduced into water, and therebythe helical shape was recovered. The Ni plating was possible accordingto the same procedure as those in Examples 1, 2.

EXAMPLE 4

The microcoil assembly obtained in Example 2 was mixed with a paperpulp, and molded into a sheet form followed by drying. Thus, anelectric-wave shield or absorbing paper having a favorable attenuationrate of 20 dB or higher in the frequency band of 1 to 10 GHz wasobtained.

POSSIBILITY OF INDUSTRIAL APPLICATION

A helical fine structure according to the present invention includes aphytoplankton having a helical shape and a surface modification layerformed on the phytoplankton, and is capable of efficient massproduction. The surface modification layer includes at least one metalplating layer. Thereby, the helical fine structure has a possibility ofindustrial applicability that it is utilized as an electric-wave shieldor an absorbing material.

1. A helical fine structure characterized by comprising: a phytoplanktonhaving a helical shape; and a surface modification layer formed on thephytoplankton.
 2. The helical fine structure according to claim 1,characterized in that the surface modification layer includes at leastone metal plating layer.
 3. The helical fine structure according toclaim 2, characterized in that an outer membrane is removed from asurface of the phytoplankton.
 4. The helical fine structure according toclaim 3, characterized in that the phytoplankton having a helical shapeis a phytoplankton selected from the group of cyanobacteria calledSpirulina and consisting of Arthrospira Platensis, Arthrospira Maxima,and Arthrospira Subsalsa belonging to Arthrospira genus.
 5. A method forproducing a helical fine structure, comprising forming a surfacemodification layer on a phytoplankton having a helical shape, the methodcharacterized in that a prestep of the step of forming the surfacemodification layer on the phytoplankton having a helical shape includesa step of removing an outer membrane from a surface of thephytoplankton.
 6. The method for producing a helical fine structureaccording to claim 5, characterized in that the step of removing theouter membrane from the surface of the phytoplankton is a washing stepwith an organic solvent.
 7. The method for producing a helical finestructure according to claim 6, characterized by comprising: a dryingstep of drying the phytoplankton having a helical shape to obtain adeformed dried phytoplankton; and a shape recovering step of permeatingthe dried phytoplankton with a polar solvent to cause the phytoplanktonto recover the same helical shape as before the drying step.
 8. Anelectric-wave shield or an absorber characterized by comprising aplurality of the helical fine structures according to claim 2electrically or magnetically connected together to form an assembly. 9.The helical fine structure according to claim 1, characterized in thatan outer membrane is removed from a surface of the phytoplankton. 10.The helical fine structure according to claim 9, characterized in thatthe phytoplankton having a helical shape is a phytoplankton selectedfrom the group of cyanobacteria called Spirulina and consisting ofArthrospira Platensis, Arthrospira Maxima, and Arthrospira Subsalsabelonging to Arthrospira genus.
 11. The helical fine structure accordingto claim 1, characterized in that the phytoplankton having a helicalshape is a phytoplankton selected from the group of cyanobacteria calledSpirulina and consisting of Arthrospira Platensis, Arthrospira Maxima,and Arthrospira Subsalsa belonging to Arthrospira genus.
 12. The helicalfine structure according to claim 2, characterized in that thephytoplankton having a helical shape is a phytoplankton selected fromthe group of cyanobacteria called Spirulina and consisting ofArthrospira Platensis, Arthrospira Maxima, and Arthrospira Subsalsabelonging to Arthrospira genus.
 13. The method for producing a helicalfine structure according to claim 5, characterized by comprising: adrying step of drying the phytoplankton having a helical shape to obtaina deformed dried phytoplankton; and a shape recovering step ofpermeating the dried phytoplankton with a polar solvent to cause thephytoplankton to recover the same helical shape as before the dryingstep.